Conductive rubber members for use in an image-forming apparatus such as an electrophotographic copying machine or printer are imparted with electrical conductivity (hereinafter referred to simply as conductivity) by use of a conductivity-imparting material such as carbon black. Such rubber members problematically exhibit variation and changes in electrical resistance. Such variation and changes in electrical resistance at the surface of a conductive rubber member result in defects in formed images such as white spots.
The present applicant previously proposed a development roller having an elastic layer which has been imparted with conductivity by carbon black, and a surface treatment layer which has been produced through treatment of the surface of the elastic layer with a surface-treating liquid containing isocyanate, wherein the electrical resistance of the surface treatment layer gradually lowers from the top surface to the interior (see Patent Document 1). In the development roller disclosed in Patent Document 1, the network structure of carbon black in the formed surface treatment layer is gradually broken from the top surface to the interior, whereby the electrical resistance of the surface treatment layer gradually lowers (i.e., resistance-gradient layer). By virtue of the thus-formed resistance-gradient layer, variation in electrical resistance is suppressed.
However, when such a surface treatment layer is produced by use of a surface-treating liquid containing no carbon black, the network structure of carbon black which was present in the elastic layer before the treatment is broken by impregnation with isocyanate, in some cases resulting in a electrical resistance higher than a desired level. In the case where the surface treatment layer is produced by use of a surface-treating liquid containing carbon black, a uniform network structure of carbon black cannot be produced from the surface-treating liquid, in some cases causing variation in electrical resistance.
Patent Document 1:
Japanese Patent Application Laid-Open (kokai) No. 2003-202750